The primary objective of this proposal is to investigate the fundamental mechanisms that regulate mammalian craniofacial development. Craniofacial morphogenesis is regulated by complex interactions between the surface and neural ectoderms, endoderm, paraxial mesoderm and cranial neural crest. This process is highly dependent on the patterning information of emigrant cranial neural crest cells. The majority of craniofacial abnormalities are caused by defects in cranial neural crest cells that give rise to a variety of facial tissues and structures, including the cranial skull. Craniosynostosis affects 1 in ~2,500 infants and is 1 of the most common human congenital craniofacial deformities. Patients with craniosynostosis exhibit abnormal calvaria that are caused by defects in development of cranial suture and skull vault. Although genetic linkage analyses have provided some information on the molecular basis of craniosynostosis-related syndromes, very little is known about the biology of suture and skull development. In this proposal, we will study the genetic regulatory network that mediates calvarial morphogenesis and craniosynostosis in genetically modified mice. We have developed several mouse strains uniquely suited for these studies. Mutation of Axin2 severely affects formation of calvarial tissues and structures that are neural crest in origin. Phenotypic defects resembling craniosynostosis in humans developed in the mutants. Because of the abilities of Axin2 to negatively regulate the Wnt pathway by modulating the cellular levels of beta-catenin, we propose that the Wnt-Axin signaling network plays an important role in calvarial morphogenesis. We will elucidate the mechanism underlying suture development mediated by this signaling network. These studies promise new insights into the molecular mechanism of craniofacial development and human diseases.